Effect of TaSi₂ and WSi₂ deposition on interfacial defects and Fowler-Nordheim injection in polycide gate SiO₂ MOS capacitors

Abstract
In this work we have studied the effect of TaSi₂ and WSi₂ silicide deposition on the electrical properties of non-degraded dry-wet-dry oxides (˜ 7.2 nm) in polycide/SiO₂/Si structures. WSi₂ and TaSi₂ silicides are deposited by chemical vapor deposition and by sputtering respectively. Particular attention has been paid to the non-uniform density (D_it) energetical distribution of amphoter Si/SiO₂ interface states, to the presence of acceptor and/or donor interface states (D_imp) due to impurities induced by the polycide gate process, and to Fowler-Nordheim (FN) barrier heights at both injecting interfaces. We have observed that i) TaSi₂ structures present more important D_it densities that WSi₂ ones, ii) TaSi₂ samples reveal the presence of acceptor D_imp interface states probably due to SiO₂ contamination by elements of the I and II groups during the silicide deposition, iii) the polycide type has a strong impact on both FN barrier heights. Finally the influence of gate oxide nitridation in N₂O has been considered both in TaSi₂ and WSi₂ structures : i) the nitridation reduces D_it density but this reduction is more pronounced in the case of TaSi₂ devices, ii) the nitridation does not reduce D_imp density in TaSi₂ structures.